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After the publication of this work[1], we became aware that the our description of the methods used to identify Shigella spp. did not describe the identification of a subset of Shigella spp. which were untypeable with commercial sera. Additional typing was conducted by Dr. Kaisar A. Talukder and coworkers (Laboratory Sciences Division, ICDDR, B: Centre for Health and Population Research, GPO Box-128, Dhaka-1000, Bangladesh. Email:kaisar@icddrb.org.)

Brief description of the methods used for serotyping the untypeable S. flexneristrains using MASF

All Shigella strains which agglutinated with commercial polyvalent anti-S. flexneri serum (Denka Seiken, Tokyo, Japan) but were untypeable using commercial serotype specific antisera were examined using a panel of monoclonal antibodies against S. flexneri (MASF B) according to the typing scheme shown in Table 1 using monoclonal antibodies from one supplier (Reagensia AB, Stockholm, Sweden) with the exception of MASF 1c which was provided by Dr. N. I. A. Carlin (SBL, Sweden) [2–5]. Untypeable S. flexneri strains which agglutinated strongly with polyclonal MASF B and type antigen factor IV-2 but not with group factor Y-5 or 6 thereby excluding their characterization into serotype 4a or 4b were designated as serotype 4 if they agglutinated with a new antigenic determinant E1037 (IV-1). Untypeable strains which agglutinated with antibodies against the provisional antigen, MASF IV-1 specific for the new antigenic determinant E1037, were designated as 4X. Untypeable strains which agglutinated only with MASF Ic were designated as 1c.

Table 1 S. flexneri serotyping criteria using MASF antibodies
Full size table